KR101009792B1 - Multiple simultaneous frequency detection - Google Patents

Abstract

It is disclosed to use multiple stimulus frequencies and phases to create an image of a touch on a touch sensor panel. Each of the plurality of sensing channels may be connected to one column of the touch sensor panel and may have multiple mixers. Each mixer in the sense channel may use circuitry that can generate a demodulation frequency of a particular frequency. In each of the plurality of steps, various phases of the selected frequency may be used to simultaneously stimulate rows of the touch sensor panel, and multiple mixers in each sense channel may be used to select each sense channel using the selected frequency. And demodulate a signal received from the connected column. After all the steps have been completed, demodulated signals from multiple mixers can be used in the calculation to obtain an image of the touch on the touch sensor panel at each frequency.

Touch sensor panel, spectral analysis, sensing channel, stimulus signal

Description

Multiple Simultaneous Frequency Detection {MULTIPLE SIMULTANEOUS FREQUENCY DETECTION}

TECHNICAL FIELD The present invention relates to a touch sensor panel used as an input device of a computing system, and more particularly to performing a spectral analysis of noise and identifying a low noise stimulation frequency. It relates to the use of digital mixers and the use of multiple stimulus frequencies and phases to detect and localize touch events in touch sensor panels.

Many types of input devices, such as buttons or keys, mice, trackballs, touch sensor panels, joysticks, touch screens, and the like, are currently available for performing operations in computing systems. In particular, touch screens are becoming more and more common due to ease of operation and variety, as well as falling prices. The touch screen may include a touch sensor panel, which may be a transparent panel having a touch sensitive surface, and a display device, which may be disposed behind the panel such that the touch sensitive surface almost covers the visible area of the display device. The touch screen allows a user to perform various functions by touching the touch sensor panel using a finger, stylus or other object at a location determined by a user interface (UI) displayed by the display device. In general, the touch screen can recognize the location of the touch event and the touch event on the touch sensor panel, and the computing device can then interpret the touch event according to the display appearing at the touch event and then based on the touch event One or more operations may be performed.

The touch sensor panel may be formed as a matrix of row and column traces, and a sensor or pixel exists where the rows and columns are separated by dielectric material and cross each other. Each row can be driven by a stimulus signal, and the touch location can be identified because the charge injected into the column due to the stimulus signal is proportional to the amount of touch. However, the high voltages that may be required for the stimulus signal result in larger sensor panel circuits that can be separated into two or more discrete chips. In addition, display devices such as touch screens and liquid crystal displays (LCDs), which are formed from capacitance-based touch sensor panels, may experience noise problems, since the voltage switching required to operate the LCD may cause This is because capacitive coupling to the columns can cause inaccurate measurements of the touch. In addition, alternating current (AC) adapters used to power or charge the system can also couple noise to the touch screen. Other noise sources may include switch power supplies, backlight inverters, and LED (light emitting diode) pulse drivers in the system. Each of these noise sources has a unique interference frequency and amplitude that can vary over time.

The present invention relates to the use of multiple digital mixers to perform spectral analysis of noise and to the use of multiple stimulus frequencies and phases to detect and localize touch events in touch sensor panels. Each of the plurality of sensing channels may be connected to a column in the touch sensor panel and may have multiple mixers. Each mixer in each sense channel may use circuitry that can be controlled to produce modulation frequencies of a particular frequency, phase and delay.

When performing the spectrum analyzer function, no stimulus signal is applied to any row in the touch sensor panel. The sum of the outputs of all sense channels, which may represent the total charge applied to the touch sensor panel, including all detected noise, may be fed back to each of the mixers in each sense channel. These mixers can be paired, and each mixer pair can demodulate the sum of all sense channels using in-phase (I) and quadrature (Q) signals at specific frequencies. have. The modulated output of each mixer pair can be used to calculate the magnitude of the noise at that particular frequency, where the smaller the magnitude, the less the noise at that frequency. Several low noise frequencies can then be selected for use in the touch sensor panel scan function.

When performing the touch sensor panel scan function, in each of the plurality of steps, various phases of the selected low noise frequencies can be used to stimulate the rows of the touch sensor panel simultaneously, and multiple mixers in each sensing channel are selected. It may be configured to demodulate a signal received from a column coupled to each sense channel using a low noise frequency. Demodulated signals from multiple mixers may then be stored. After all steps have been completed, the stored results can be used in the calculation to obtain an image of the touch on the touch sensor panel at each frequency.

In the following description of the preferred embodiments, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. It will be appreciated that other embodiments may be used and structural changes may be made without departing from the scope of the embodiments of the present invention.

The present invention is directed to using multiple digital mixers to perform spectral analysis of noise and to identify low noise stimulus frequencies, and to use multiple stimulus frequencies and phases to detect and localize touch events on touch sensor panels. It is about. Each of the plurality of sensing channels may be connected to a column in the touch sensor panel and may have multiple mixers. Each mixer in the sense channel can use circuits that can be controlled to produce demodulation frequencies of a particular frequency, phase, and delay.

When performing the spectrum analyzer function, no stimulus signal is applied to any row of the touch sensor panel. The sum of the outputs of all sense channels that can represent the total charge applied to the touch sensor panel, including all detected noise, can be fed back to each of the mixers in each sense channel. These mixers can be paired, and each mixer pair can demodulate the sum of all sense channels using in-phase (I) and quadrature (Q) signals at specific frequencies. have. The modulated output of each mixer pair can be used to calculate the magnitude of the noise at that particular frequency, where the smaller the magnitude, the less the noise at that frequency. Several low noise frequencies can then be selected for use in the touch sensor panel scan function.

When performing the touch sensor panel scan function, in each of the plurality of steps, various phases of the selected low noise frequencies can be used to stimulate the rows of the touch sensor panel simultaneously, and multiple mixers in each sense channel are selected for low noise. The frequency can be configured to demodulate a signal received from a column coupled to each sense channel. Demodulated signals from multiple mixers may then be stored. After all steps have been completed, the stored results can be used in the calculation to obtain an image of the touch on the touch sensor panel at each frequency.

Although some embodiments of the present invention may be described herein with reference to a mutual capacitance touch sensor, embodiments of the present invention are not so limited and generally are self capacitance touch sensors. It will be appreciated that it is applicable to other types of touch sensors, such as). In addition, although touch sensors in a touch sensor panel may be described herein with reference to an orthogonal array of touch sensors having rows and columns, embodiments of the present invention are not limited to orthogonal arrays and are generally diagonal. It will be appreciated that it may be applicable to touch sensors arranged in any number of dimensions and orientations, including concentric circles, and three-dimensional and random orientations. In addition, the touch sensor panel described herein can be a single-touch or multi-touch sensor panel, filed May 6, 2004 for the multi-touch sensor panel, and issued in the United States on May 11, 2006. The present invention, published as published application 2006/0097991, is described in co-pending US patent application Ser. No. 10 / 842,862, entitled "Multipoint Touchscreen," the contents of which are herein incorporated by reference. The entire contents of which are incorporated herein by reference.

1 illustrates the use of multiple digital mixers to perform spectral analysis of noise and to identify low noise stimulus frequencies, and to detect and localize touch events in a touch sensor panel, in accordance with embodiments of the present invention. Exemplary computing system 100 that can utilize stimulus frequency and phase is shown. Computing system 100 may include one or more panel processors 102, peripherals 104, and panel subsystem 106. One or more panel processors 102 may include, for example, an ARM968 processor or other processor having similar functionality and performance. However, in other embodiments, panel processor functionality may instead be implemented by dedicated logic, such as a state machine. Peripheral device 104 may include, but is not limited to, random access memory (RAM) or other types of memory or storage, watchdog timers, and the like. Panel subsystem 106 may include, but is not limited to, one or more sense channels 108, channel scan logic 110, and driver logic 114. The channel scan logic 110 can access the RAM 112, autonomously read data from the sense channel, and provide control over the sense channel. In addition, the channel scan logic 110 can control the driver logic 114 to generate stimulus signals 116 at various frequencies and phases that can be selectively applied to rows of the touch sensor panel 124. . In some embodiments, panel subsystem 106, panel processor 102 and peripheral 104 may be integrated into a single application specific integrated circuit (ASIC).

The touch sensor panel 124 includes a capacitive sensing medium having a plurality of row traces or driving lines and a plurality of column traces or sensing lines. Although other sensing media may be used. The row wiring and the column wiring may be formed of a transparent conductive medium such as indium tin oxide (ITO) or antimony tin oxide (ATO), but other transparent materials and opaque materials such as copper may also be used. In some embodiments, the row wiring and the column wiring can be perpendicular to each other, but other non-Cartesian orientations are possible in other embodiments. For example, in polar coordinates, the sense line can be concentric and the drive line can be a radially extending line (or vice versa). Thus, the terms "row" and "column", "first dimension" and "second dimension" or "first axis" and "second axis", as used herein, are orthogonal grids. It will also be appreciated that it is intended to include intersecting interconnections (concentric lines and radial lines of polar arrays) of different geometric configurations as well as the first and second dimensions. Rows and columns may be formed on one side of the substantially transparent substrate separated by a substantially transparent dielectric material, on both sides of the substrate, or on two separate substrates separated by the dielectric material.

At the "intersection point" of the wires where the wires pass up and down each other (intersect each other) (no direct electrical contact with each other), these wires can essentially form two electrodes (but can cross three or more wires as well). ). Each intersection of the row wiring and the column wiring can represent a capacitive sensing node and can be viewed as a pixel (pixel) 126, which the touch sensor panel 124 captures the "image" of the touch. It can be particularly useful when viewed. (In other words, after the panel subsystem 106 determines that a touch event has been detected at each touch sensor in the touch sensor panel, the pattern of touch sensors in the multi-touch panel generated by the touch event is the “image” of the touch. (E.g., a pattern of fingers touching a panel). The capacitance between a row electrode and a column electrode appears as a leakage capacitance when a given row is maintained at a direct current (DC) voltage level and is given by When a row is stimulated with an alternating current (AC) signal, it appears as mutual signal capacitance Csig. The presence of a finger or other object near or on the touch sensor panel can be detected by measuring the change in signal charge Qsig present in the pixel being touched, which is a function of Csig. Each column of touch sensor panel 124 may drive a sense channel 108 (also referred to herein as event detection and demodulation circuitry) in panel subsystem 106.

The computing system 100 also receives output from the panel processor 102 and moves, scrolls or pans, adjusts control settings, opens a file or document, and moves an object such as a cursor or pointer. , Viewing menus, making selections, executing commands, operating peripheral devices connected to the host device, answering calls, placing calls, ending phone calls, volume or audio settings Changing, storing phone-related information, such as addresses, frequently dialed numbers, received calls, missed calls, logging on to a computer or computer network, and to authorized individuals Or allowing access to restricted areas of the computer network, loading user profiles associated with the user's preferred configuration of the computer desktop, web content A host processor 128 that performs operations based on output that may include, but is not limited to, allowing access to the software, launching a particular program, encrypting or decoding a message, and the like. can do. The host processor 128 may also be coupled to a display device 130, such as an LCD display that performs additional functions that may not be related to panel processing and provides a UI to the user of the device. have.

In some systems, sensor panel 124 may be driven with high voltage driver logic. Due to the high voltages (e.g. 18V) that may be required by the high voltage driver logic, the panels may inevitably operate at much lower digital logic voltage levels (e.g. 1.7 to 3.3V). It may have to be formed separately from subsystem 106. However, in embodiments of the present invention, on-chip driver logic 114 may replace off-chip high voltage driver logic. While panel subsystem 106 may have a low digital logic level supply voltage, on-chip driver logic 114 cascades two transistors with each other to form charge pump 115. It is possible to produce a supply voltage greater than the level supply voltage. Charge pump 115 may be used to generate stimulation signal 116 ((Vstim)) which may have an amplitude of about twice the digital logic level supply voltage (eg, 3.4 to 6.6 V). Can be. Although FIG. 1 illustrates charge pump 115 separately from driver logic 114, the charge pump may be part of the driver logic.

2A illustrates an exemplary mutual capacitance touch sensor panel 200 in accordance with embodiments of the present invention. FIG. 2A shows the presence of leakage capacitance Cstray at each pixel 202 at the intersection of the row interconnection 204 and the column interconnection 206 (although in FIG. 2A only one column is shown to simplify the drawing). Only Cstray is shown). In the example of FIG. 2A, AC stimulus Vstim 214, Vstim 215, and Vstim 217 may be applied to several rows, while other rows may be connected to DC. Vstim 214, Vstim 215 and Vstim 217 may be at different frequencies and phases, which will be described later. With each stimulus signal in a row, charge Qsig = Csig x Vstim can be injected into the columns through the mutual capacitance present in the affected pixels. The change in injected charge Qsig_sense can be detected when the finger, palm or other object is present in one or more affected pixels. Vstim signals 214, 215, and 217 may include one or more sine wave bursts. Note that while FIG. 2A shows the rows 204 and columns 206 as nearly vertical, they do not need to be so aligned as described above. As noted above, each column 206 may be connected to a sense channel (see sense channel 108 of FIG. 1).

2B is a side view of an exemplary pixel 202 in a steady-state (no touch) condition in accordance with embodiments of the present invention. In FIG. 2B, an electric field line 208 of mutual capacitance between the column wires or electrodes 206 and the row wires or electrodes 204 separated by the dielectric 210 is shown.

2C is a side view of an example pixel 202 in a dynamic (touch) condition. In FIG. 2C, finger 212 is located near pixel 202. Finger 212 is a low impedance object at signal frequencies and has an AC capacitance Cfinger from thermal wiring 204 to the body. The body has a magnetic capacitance Cbody to ground of about 200 pF, which is much larger than the Cfinger. If finger 212 blocks any field line 208 between the row and column electrodes (a fringing field that exits the dielectric and passes through the air above the row electrode), the field line Branching to ground through the capacitance path inherent in the body results in a reduction of the steady-state signal capacitance Csig by ΔCsig. In other words, the combined body and finger capacitance acts to reduce Csig by ΔCsig (also referred to herein as Csig_sense) and to ground off part of the electric field resulting in a reduction in net signal capacitance. Act as a shunt or dynamic return path to the furnace. The signal capacitance at the pixel is Csig-ΔCsig, where Csig represents a static (no touch) component and ΔCsig represents a dynamic (touch) component. Note that Csig-ΔCsig may not always be zero because fingers, palms or other objects cannot block all electric fields, especially those that are completely within the dielectric material. In addition, when a finger is pressed harder or more fully on the multi-touch panel, the finger may be flat and tend to block more electric field, thus ΔCsig may be variable and how completely the finger is pressing on the panel. (Ie, a range from "no touch" to "full-touch").

3A illustrates a portion of an exemplary sense channel or event detection and demodulation circuit 300 in accordance with embodiments of the present invention. One or more sense channels 300 may be present in the panel subsystem. Each column of the touch sensor panel may be connected to the sensing channel 300. Each sense channel 300 includes a virtual-ground amplifier 302, an amplifier output circuit 309 (described in greater detail below), a signal mixer 304, and an accumulator ( 308). Note that the amplifier output circuit 309 may also be connected to other signal mixers and associated circuits not shown in FIG. 3A to simplify the drawing.

The virtual-ground amplifier 302, which may also be referred to as a DC amplifier or a charge amplifier, may include a feedback capacitor Cfb and a feedback resistor Rfb. In some embodiments, Cfb can be made much smaller than in any previous design because the amount of charge that can be injected into the heat due to the low Vstim amplitude is much smaller. However, in other embodiments, Cfb is not reduced in size because all rows can be stimulated at the same time (which tends to add charge).

3A shows a total steady-state that may be contributed by a touch sensor panel column connected to the sensing channel 300 when one or more input stimulus Vstim is applied to one or more rows of touch sensor panels and no fingers, palms or other objects are present. Total steady-state signal capacitance Csig_tot is indicated by a dotted line. In steady state, i.e. no touch condition, the total signal charge Qsig_tot injected into the column is the sum of all the charges injected into the column by each stimulated row. In other words, Qsig_tot = Σ (Csig * Vstim for all stimulated rows). Each sensing channel connected to a column can detect a change in the total signal charge due to the presence of a finger, palm or other body part or object in one or more pixels in that column. In other words, Qsig_tot_sense = Σ ((Csig-Csig_sense) * Vstim for all stimulated rows)

As noted above, each pixel on the touch sensor panel may have an inherent stray capacitance Cstray. In the virtual ground charge amplifier 302, when the + (non-inverting) input is connected to the reference voltage Vref, the-(inverting) input may also be driven to Vref, and a DC operating point may be set. Thus, regardless of how much Csig is present at the input to the virtual ground charge amplifier 302, the input can always be driven to Vref. Due to the nature of the virtual ground charge amplifier 302, the charge Qstray stored in the Cstray is constant because the voltage across the Cstray is kept constant by the charge amplifier. Thus, no matter how much leakage capacitance Cstray is added to the-input, the net charge to Cstray is always zero. Thus, the input charge is zero when the corresponding row is held at DC and is purely a function of Csig and Vstim when the corresponding row is stimulated. In either case, because there is no charge through Csig, leakage capacitance is eliminated and essentially missing from all equations. Thus, even when there is a hand on the touch sensor panel, the Cstray may increase, but the output is not affected by the charge of the Cstray.

The gain of the virtual ground amplifier 302 can be small (eg, 0.1) and can be calculated as the ratio of Csig_tot and feedback capacitor Cfb. Adjustable feedback capacitor Cfb can convert charge Qsig to voltage Vout. The output Vout of the virtual ground amplifier 302 is a voltage that can be calculated by multiplying the ratio of -Csig / Cfb by Vstim connected to Vref. Vstim signaling may thus appear at the output of the virtual ground amplifier 302 as a signal with a smaller amplitude. However, if a finger is present, the amplitude of the output can be reduced even further, because the signal capacitance is reduced by ΔC sig. The output of the charge amplifier 302 is a superposition of all the row stimulus signals multiplied by each of the Csgi values in the columns associated with that charge amplifier. A column can have several pixels driven at a frequency of plus phase, while at the same time other pixels driven at the same frequency of negative phase (ie 180 degrees out of phase). In this case, the total component of the charge amplifier output signal at that frequency may be the amplitude and phase associated with the sum of the product of each of the Csig values multiplied by each of the stimulus waveforms. For example, if two rows are driven in a positive phase and two rows are driven in a negative phase and the Csig values are all the same, then the total output signal is zero. As the finger approaches one of the pixels being driven in positive phase and the associated Csig decreases, the total output at that frequency has a negative phase.

Vstim applied to the rows of the touch sensor panel can be generated as a burst of sine waves (eg, sine waves with amplitudes that vary slowly to be narrow spectrum) or other non-DC signaling on other DC signals. However, in some embodiments, a sine wave representing Vstim may come before and after other non-DC signaling. If Vstim is applied in a row and there is signal capacitance in the column connected to the sense channel 300, then the output of the charge amplifier 302 associated with that particular stimulus may be one of the moisture of the pp amplitude of Vstim (this ratio is Corresponding to the gain of charge amplifier 302) may be a sine wave train 310 centered on Vref having a peak-peak (pp) amplitude in steady-state conditions. For example, if Vstim contains a 6.6V p-p sine wave and the gain of the charge amplifier is 0.1, the output of the charge amplifier associated with this row may be approximately 0.67V p-p sine file. Note that the signals from all rows overlap at the output of the preamplifier. The analog output from the preamplifier is converted to digital at block 309. The output from 309 can be mixed with demodulated waveform Fstim 316 in digital signal mixer 304 (which is a digital multiplier).

Since Vstim can produce undesirable harmonics, especially when formed from square waves, demodulation waveform Fstim 316 is digitally generated from numerically controlled oscillator (NCO) 315. It can be a Gaussian sine wave that can be synchronized to Vstim. In addition to the NCO 315 used for digital demodulation, it will be appreciated that an independent NCO can be connected to a digital-to-analog converter (DAC) and its output can be selectively inverted and used as a row stimulus. The NCO 315 may include a numerical control input that sets the output frequency, a control input that sets the delay, and a control input that enables the NCO to generate an in-phase (I) or quadrature (Q) signal. Signal mixer 304 may demodulate the output of charge amplifier 310 by subtracting Fstim 316 from the output to provide better noise rejection. Signal mixer 304 may suppress all frequencies outside the pass band (in one example, it may be about +/− 30 kHz around Fstim). Such noise suppression can be beneficial in noisy environments with many noise sources, such as 802.11, Bluetooth, etc., all of which have certain characteristic frequencies that can interfere with the sensitive (femtofarad level) sense channel 300. For each channel of interest to be demodulated, the signal mixer 304 is essentially a synchronous rectifier because the frequency of the signal at its input is the same, and as a result, the signal mixer output 314 is essentially This is because it is a rectified Gaussian sine wave.

3B illustrates a simplified block diagram of N exemplary sense channels or event detection and demodulation circuits 300 in accordance with embodiments of the present invention. As noted above, each charge amplifier or programmable gain amplifier (PGA) in the sense channel 300 may be connected to an amplifier output circuit 309, which in turn is a multiplexer. 303 may be connected to R signal mixers 304. The amplifier output circuit 309 may include an anti-aliasing filter 301, an ADC 303, and a result register 305. Each signal mixer 304 may be demodulated with a signal from a separate NCO 315. The demodulated output of each signal mixer 304 may be coupled to separate accumulator 308 and result register 307.

The PGA 302, which can detect the high amount of charge generated from the high voltage Vstim signal (e.g., 18V), can now detect the lower amount of charge generated from the lower voltage Vstim signal (e.g., 6.6V). You will know well. In addition, the NCO 315 allows the output of the charge amplifier 302 to be demodulated at the same time but differently, since each NCO 310 can generate signals at different frequencies, delays and phases. . While each signal mixer 304 in a particular sense channel 300 can thus produce an output that represents approximately 1 / R of the charge of the previous design, R mixers each demodulating at different frequencies As such, each sense channel can still detect approximately the same total charge amount as in the previous design.

In FIG. 3B, the signal mixer 304 and accumulator 308 may be digitally implemented instead of analog circuitry within the ASIC. The digital implementation of the mixer and accumulator instead of analog circuitry inside the ASIC can save about 15% of die space.

3C illustrates an exemplary block diagram of ten sense channels 300 that can be configured as spectrum analyzer or as panel scan logic, in accordance with embodiments of the present invention. In the example of FIG. 3C, each of the ten sensing channels 300 may be connected to different columns of the touch sensor panel. Note that each sense channel 300 may include a multiplexer or switch 303, as described in more detail below. In FIG. 3C, the solid line connection may represent a sense channel configured as panel scan logic, and the dotted line connection may represent a sense channel configured as a spectrum analyzer. 3c will be described in more detail later.

4A illustrates an exemplary timing diagram 400 illustrating LCD step 402 and vertical blanking or touch sensor panel step 404 in accordance with embodiments of the present invention. During LCD step 402, the LCD may be actively switching and generating the voltage needed to generate the image. Panel scanning is not performed at this time. During touch sensor panel step 404, the sense channel may be configured as a spectrum analyzer to identify low noise frequencies and may also be configured as panel scan logic to detect and locate images of touch.

4B illustrates an exemplary flow diagram 406 illustrating LCD step 402 and touch sensor panel step 404 corresponding to the example of FIG. 3C (example here), in accordance with embodiments of the present invention. In step 0, the LCD may be updated as follows.

Steps 1 through 3 may represent a low noise frequency identification step 406. In step 1, the sense channel can be configured as a spectrum analyzer. The purpose of the spectrum analyzer is to identify some low noise frequencies for later use in panel scans. If a stimulus frequency is not applied to any of the rows of the touch sensor panel, the sum of the outputs of all sense channels, representing the total charge applied to the touch sensor panel, including all detected noise, is present in each sense channel. It can be fed back to each of the mixers. The mixers can be paired, and each mixer pair can demodulate the sum of all sense channels using in-phase (I) and quadrature (Q) signals of a particular frequency. . The modulated output of each mixer pair can be used to calculate the magnitude of the noise at that particular frequency, where the smaller the magnitude, the less the noise at that frequency.

In step 2, the process of step 1 can be repeated for a different series of frequencies.

In step 3, several low noise frequencies can be selected for use in subsequent touch sensor panel scans by identifying the frequency that produces the lowest calculated magnitude value.

Steps 4 through 19 may represent panel scan step 408. In steps 4 through 19, the sense channel can be configured as panel scan logic. In each of steps 4 to 19, different phases of the selected low noise frequency can be used to simultaneously stimulate the rows of the touch sensor panel, and multiple mixers in each sense channel can be used to select each noise channel using the selected low noise frequency. And may demodulate a signal received from the connected column. Demodulated signals from multiple mixers can then be stored.

In step 20, after all steps are completed, the stored results can be used in the calculation to obtain an image of the touch on the touch sensor panel at each of the selected low noise frequencies.

Referring again to the example here shown in FIG. 3C, although the sense channel 300 is configured as a spectrum analyzer, no stimulus signal is applied to any of the rows of the touch sensor panel. In this example, there are ten rows and thus ten sense channels 300, three mixers 304 for each sense channel 300, a total of thirty mixers. The outputs of all amplifier output circuits 309 in all sense channels 300 may be summed together using a summing circuit 340 and configured to select the output of the summing circuit 340 instead of the charge amplifier 302. May be fed to all mixers 304 through a multiplexer or switch 303 which may be.

While the sense channel is configured as a spectrum analyzer, the background coupling to the columns can be measured. Since no Vstim is applied to any row, there is no Csig on any pixel, and no touch on the panel (unless the touching finger or other object couples noise to ground) must affect the noise result. By adding up all the outputs of all the amplifier output circuits 309 to each other in the adder 340, one digital bitstream representing the total noise received by the touch sensor panel can be obtained. Before the spectral analysis, the frequency of the noise and the pixels from which the noise is generated are not known, but after the spectral analysis is completed. The pixels from which noise is generated are not known and are not recovered after spectral analysis, but because the bitstream is used as a general noise collector, it is not necessary to know them.

While configured as a spectrum analyzer, 30 mixers in the example of FIG. 3C can be used in 15 pairs, each pair demodulating I and Q signals for 15 different frequencies generated by the NCO 315. do. These frequencies may be between 200 kHz and 300 kHz, for example. The NCO 315 can generate a digital rampsine wave that can be used by the digital mixer 304 to demodulate the noise output of the summing circuit 340. For example, NCO 315_0_A can generate the I component of the frequency FO, while NCO 315_0_B can produce the Q component of the FO. Similarly, NCO 315_0_C can generate an I component of frequency F1, NCO 3l5_l_A can produce a Q component of F1, NCO 315_l_B can produce an I component of frequency F2, and NCO 315_1_C is a Q of F2. A component can be produced and it is the same below.

The output of the summing circuit 340 (noise signal) can then be demodulated by the I and Q components of F0 through F14 using 15 pairs of mixers. The results of each mixer 304 may accumulate in accumulator 308. Each accumulator 308 may be a digital register capable of accumulating (summing) instantaneous values from the mixer 304 over a sample period. At the end of the sample period, the accumulated value represents the amount of noise signal at that frequency and phase.

The cumulative result of I and Q demodulation at a particular frequency may indicate the amount of content at that frequency that is in phase or quadrature. These two values may then be used in magnitude and phase calculation circuit 342 to find the absolute value of the total magnitude (amplitude) at that frequency. Higher magnitude may mean a higher background noise level at that frequency. The magnitude value calculated by each magnitude and phase calculation circuit 342 may be stored. Note that Q component noise that is out of phase with the demodulation frequency may remain undetected.

This entire process can be repeated for 15 different frequencies F15-F29. The magnitude values stored for each of the 30 frequencies can then be compared and three frequencies with the smallest magnitude values (and therefore the lowest noise level) (herein referred to as frequencies A, B and C) can be selected. . In general, the number of selected low noise frequencies may correspond to the number of mixers in each sense channel.

Still referring to FIG. 3C, when the sense channel 300 is configured as panel scan logic, the dashed line in FIG. 3C can be ignored. In each of steps 4 to 19, various phases of the selected low noise frequency can be used to simultaneously stimulate the rows of the touch sensor panel, and a plurality of mixers in each sense channel using the selected low noise frequencies A, B and C And demodulate a signal received from a column coupled to each sense channel. In the example of FIG. 3C, NCO_0_A can generate frequency A, NCO_0_B can generate frequency B, NCO_0_C can generate frequency C, NCO_I_A can generate frequency A, and NCO_I_B is frequency B May be generated, and NCO_I_C may generate a frequency C, which is the same below. The demodulated signal from each mixer 304 in each sense channel can then be accumulated and stored in accumulator 308.

In general, the R mixer outputs for any sense channel M (where M = 0 to N-1) demodulated by _R low noise frequencies F ₀ , F ₁ ... F _R-1 are notation xF ₀ S [chM], xF ₁ S [chM] ... can be expressed as xF _R-1 S [chM], where xF ₀ represents the output of the mixer demodulated at frequency F ₀ , and xF ₁ demodulated to frequency F1 Represents the output of the mixer, xF _R-1 represents the output of the mixer demodulated at frequency F _R-1 , and S represents the sequence number in the panel scan step.

Thus, in step 4 (representing sequence number 1 in the panel scan step), using the low noise frequencies A, B and C as demodulation frequencies, the output to be stored is xal [chO], xb1 [chO], xc1 [chO], xal [ch1], xb1 [chl], xc1 [ch1], ... xal [ch9], xbl [ch9] and xc1 [ch9]. Thus, in this example, 30 results are stored in step 4. In step 5 (representing sequence number 2 in the panel scan step), the 30 results to be stored are xa2 [chO], xb2 [chO], xc2 [chO], xa2 [chl], xb2 [chl], xc2 [chl] , ... xa2 [ch9], xb2 [ch9], xc2 [ch9]. The 30 outputs to be stored in each of steps 6 to 19 may be named similarly.

It will be appreciated that additional logic outside the sense channel in FIG. 3C may be implemented in channel scan logic 110 in FIG. 1, but it may be elsewhere.

4C illustrates an exemplary capacitive scanning plan 410 corresponding to the example herein in accordance with embodiments of the present invention. FIG. 4C describes steps 0 through 19 shown in FIG. 4B for an exemplary sensor panel with 15 rows R0-R14.

Step 0 may indicate the LCD level when the LCD is updated. The LCD phase can take about 12ms, during which no row can be stimulated.

Steps 1 through 19 may indicate the vertical blanking interval for the LCD, during which time the LCD does not change the voltage.

Steps 1 through 3 may represent a low noise frequency identification step that may take about 0.6 ms, and again, no row can be stimulated during this time. In step 1, the I and Q components of different frequencies (at least 10 kHz apart) in the range of 200 kHz to 300 kHz can be applied simultaneously to the pair of mixers in the sense channel configured as the spectrum analyzer and at that frequency The magnitude of the noise can be stored. In step 2, I and Q components of different frequencies in the range of 300 kHz to 400 kHz can be applied simultaneously to a pair of mixers in a sense channel configured as a spectrum analyzer, and the magnitude of noise at that frequency can be stored. have. In step 3, the lowest noise frequencies A, B and C can be identified by finding the frequency that produced the lowest stored magnitude. The identification of the lowest noise frequency may be done only for the spectrum measured in steps 1 and 2, or may also take into account past measurements from steps 1 and 2 of the previous frame.

Steps 4 through 19 may represent panel scan steps that may take about 3.4 ms.

In step 4, which can take about 0.2 ms, the plus and minus phases of A, B and C can be applied to certain rows, while the other rows can be left unstimulated. + A can represent scan frequency A with positive phase, -A can represent scan frequency A with negative phase, + B can represent scan frequency B with positive phase, and -B can be negative phase It will be appreciated that the scan frequency B may have a scan frequency B, where + C may represent a scan frequency C with a positive phase, and -C may represent a scan frequency C with a negative phase. The charge amplifier in the sense channel connected to the columns of the sensor panel can detect the total charge connected to the column as the rows are stimulated. The output of each charge amplifier can be demodulated by three mixers in the sense channel, each mixer receiving demodulation frequencies A, B or C. The result or values xal, xbl and xc1 can be obtained and stored, where xal, xb 1 and xc1 are vectors. For example, xa1 can be a vector with 10 values xal [chO], xal [ch1], xal [ch2] ... xal [ch9], and xb1 is 10 values xb1 [chO], xb1 [ch 1], xb1 [ch2] ... xb1 [ch9], and xc1 is a vector with 10 values xc1 [chO], xc1 [chl], xc1 [ch2] ... xc1 [ch9] Can be.

Specifically, in step 4, + A is applied to rows 0, 4, 8 and 12, + B, -B, + B and -B are applied to rows 1, 5, 9 and 13, respectively, and + C , -C, + C and -C are applied to rows 2, 6, 10 and 14, respectively, and no stimulus is applied to rows 3, 7, 11 and 15, respectively. A sense channel connected to column 0 senses the charge injected into column 0 from all stimulated rows at the noted frequency and phase. The three mixers in the sense channel can now be set to demodulate A, B and C, and three different vector results xal, xb1 and xc1 can be obtained from the sense channel. For example, the vector xal may represent the sum of charges injected into columns 0-9 in four rows (eg, rows 0, 4, 8 and 12) stimulated by + A. However, the vector xa1 does not provide complete information because it still does not know the specific row where the touch occurred. In parallel, in the same step 4, rows 1 and 5 can be stimulated with + B, rows 9 and 13 can be stimulated with -B, and the vector xb1 is stimulated with + B and -B (e.g., , Rows 1, 5, 9 and 13) can represent the sum of charges injected into columns 0-9. In parallel, in the same step 4, rows 2 and 14 can be stimulated with + C, rows 6 and 10 can be stimulated with -C, and the vector xc1 is stimulated with + C and -C (e.g., , Rows 2, 6, 10, and 14) may represent the sum of charges injected into columns 0-9. Thus, at the end of step 4, three vectors, each containing ten results, a total of thirty results are obtained and stored.

Steps 5-19 are similar to step 4 except that different phases of A, B and C can be applied to different rows and different vector results are obtained at each step. At the end of step 19, a total of 480 results are obtained in the example of FIG. 4C. By acquiring 480 results in each of steps 4-19, a combinatorial and factorial method is used, in which case it is progressively applied to the image of the touch for each of the three frequencies A, B and C for each pixel. Information is obtained.

Note that step 4-19 represents a combination of two features, multi-phase scanning and multi-frequency scanning. Each feature can have its own advantages. Multi-frequency scanning can save three times as much time, while multi-phase scanning can provide about two times better signal-to-noise ratio (SNR).

Multi-phase scanning can be used by simultaneously stimulating most or all of the rows using different phases of multiple frequencies. Multi-phase scanning is described in co-pending US patent application Ser. No. 11 / 619,433, entitled “Simultaneous Sensing Arrangement,” filed Jan. 3, 2007, which application The entire contents are incorporated herein by reference herein. One advantage of multi-phase scanning is that more information can be obtained from one panel scan. Multi-phase scanning can achieve more accurate results because the possibility of inaccuracies that can be generated due to some alignment of the stimulus frequency and the phase of the noise is minimized.

In addition, multi-frequency scanning can be used by simultaneously stimulating most or all of the rows using multiple frequencies. As mentioned above, multi-frequency scanning saves time. For example, in some previous methods, fifteen rows can be scanned in fifteen steps at frequency A, followed by fifteen rows in fifteen steps in frequency B, followed by fifteen rows in frequency. It can be scanned in 15 steps in C, totaling 45 steps. However, using the multi-frequency scanning shown in the example of FIG. 4C, only a total of 16 steps (steps 4 through 19) may be needed. The multi-frequency, in the simplest embodiment, simultaneously scans R0 at frequency A, R1 at frequency B and R2 at frequency C in step 1, and R1 at frequency A, R2 at frequency B and R3 at frequency C in step 2 A total of 15 steps can be included, such as scanning at the same time.

At the end of step 4-19, when the above 480 results are obtained and stored, additional calculations may be performed using these 480 results.

4D illustrates an exemplary calculation for a particular channel M for calculating the overall image result at different low noise frequencies corresponding to the example of excitation in accordance with embodiments of the present invention. In the example here, for each channel M (where M = 0 to 9), the 45 calculations shown in FIG. 4D are obtained to obtain the row results for each row and for each frequency A, B and C. Can be performed. Each of the 45 sets of calculations for each channel may produce the resulting pixel value for the column of pixels associated with that channel. For example, row 0, frequency A calculation (xal [chM] + xa2 [chM] + xa3 [chM] + xa4 [chM]) / 4 may generate row 0, channel M results for frequency A. In this example, after all calculations have been performed and stored for all channels, a total of 450 results are obtained. These calculations correspond to step 20 of FIG. 4B.

Of these 450 results, there are 150 for frequency A, 150 for frequency B, and 150 for frequency C. The 150 results for a particular frequency represent the image of the image map or touch at that frequency because a unique value is provided for each column (ie channel) and row intersection. These touch images can then be processed by software that synthesizes three images, looks at their characteristics and determines which frequencies are inherently noisy and which frequencies are inherently clean. Further processing can then be performed. For example, if all three frequencies A, B and C are relatively noisy, the results can all be averaged.

Although the calculations shown in FIGS. 4C and 4D may be performed under the control of panel processor 102 or host processor 128 of FIG. 1, it will be appreciated that they may be performed elsewhere.

FIG. 5A identifies and touches a touch sensor panel 524, a display device 530 bonded to a sensor panel using a pressure sensitive adhesive (PSA) 534, and a low noise stimulus frequency, in accordance with embodiments of the present invention. Exemplary mobile phone 536 may be included that may include other computing system blocks within computing system 100 of FIG. 1 that apply multiple stimulus frequencies and phases to a touch sensor panel to detect and localize an event.

FIG. 5B identifies and touches a touch sensor panel 524, a display device 530 bonded to the sensor panel using a pressure sensitive adhesive (PSA) 534, and a low noise stimulation frequency, in accordance with embodiments of the present invention. Exemplary digital audio / video player 540 that may include other computing system blocks within computing system 100 of FIG. 1 that apply multiple stimulus frequencies and phases to the touch sensor panel to detect and localize an event. It is shown.

While embodiments of the invention have been described in detail with reference to the accompanying drawings, it will be appreciated that various changes and modifications will be apparent to those skilled in the art. It will be appreciated that such changes and modifications fall within the scope of the embodiments of the invention as defined by the appended claims.

1 illustrates the use of multiple digital mixers to perform spectral analysis of noise and to identify low noise stimulus frequencies, and to detect and localize touch events in touch sensor panels, in accordance with one embodiment of the present invention. Exemplary computing system that can utilize stimulus frequency and phase.

2A illustrates an exemplary mutual capacitance touch sensor panel in accordance with one embodiment of the present invention.

2B is a side view of an exemplary pixel in a steady-state condition (no touch) in accordance with one embodiment of the present invention.

2C is a side view of an exemplary pixel in a dynamic (touch) condition in accordance with one embodiment of the present invention.

3A illustrates a portion of an exemplary sense channel or event detection and demodulation circuit, in accordance with an embodiment of the invention.

3B is a simplified block diagram of N exemplary sense channels or event detection and demodulation circuits in accordance with an embodiment of the present invention.

3C is an exemplary block diagram of ten sense channels that may be configured as spectrum analyzer or panel scan logic in accordance with an embodiment of the present invention.

4A is an exemplary timing diagram illustrating LCD phase and touch sensor panel phase in accordance with an embodiment of the present invention.

4B is an exemplary flow chart illustrating LCD phase and touch sensor panel phase in accordance with one embodiment of the present invention.

4C illustrates an exemplary capacitive scanning plan in accordance with one embodiment of the present invention.

4D illustrates an exemplary calculation for a particular channel M for computing the overall image results at different low noise frequencies in accordance with one embodiment of the present invention.

5A illustrates the use of multiple digital mixers to perform spectral analysis of noise and to identify low noise stimulus frequencies, and to detect and localize touch events in touch sensor panels, in accordance with one embodiment of the present invention. Exemplary mobile telephone that may utilize stimulus frequency and phase.

5B illustrates the use of multiple digital mixers to perform spectral analysis of noise and to identify low noise stimulus frequencies, and to detect and localize touch events in touch sensor panels, in accordance with one embodiment of the present invention. Exemplary digital audio player capable of utilizing stimulus frequency and phase.

Claims (33)

A method of obtaining a plurality of values used to generate an image of a touch from a touch sensor panel, Simultaneously applying a plurality of stimulation frequencies to a plurality of drive lines of the touch sensor panel in a specific distribution, wherein the plurality of stimulation frequencies are in positive and negative phases of at least one of the stimulation frequencies; Contains all-, Receiving a signal through a different sense channel from each of the plurality of sense lines of the touch sensor panel; Demodulating the signal received on each sensing channel into a plurality of demodulation frequencies, wherein the demodulation frequency is the same frequency and in phase with the stimulation frequency; Accumulating the signals demodulated at the plurality of demodulation frequencies in each sense channel to produce a plurality of values representing the accumulated demodulated signal for each sense channel; and Storing the plurality of values for all sense channels How to include. The method of claim 1, further comprising selecting and applying multiple inherent distributions of the plurality of stimulus frequencies to the plurality of drive lines simultaneously and storing the plurality of values after applying each of the plurality of intrinsic distributions. How to include. The method of claim 2, further comprising: calculating and storing driving line results for each driving line and each of the plurality of demodulation frequencies using the stored plurality of values for each of the plurality of sensing lines. How to. 3. The method of claim 2, wherein the plurality of demodulation frequencies is a selected low noise frequency. The method of claim 1, further comprising obtaining the plurality of values during a vertical blanking step of a liquid crystal display (LCD) adjacent the touch sensor panel. A method for acquiring a plurality of values used to generate an image of a touch in a system comprising a sensor panel having a plurality of drive lines driven simultaneously with a plurality of stimulus frequencies, in a particular distribution, the method comprising: The plurality of stimulus frequencies includes both a plus and a minus phase of at least one of the stimulus frequencies, The method, Demodulating a sensing signal received on each sensing line of the sensor panel into a plurality of demodulation frequencies, wherein the demodulation frequency has the same frequency as the stimulation frequency and is in phase; and Accumulating each of the plurality of demodulated sense signals for each sense line to generate the plurality of values representing the accumulated demodulated sense signals. How to include. The method of claim 6, wherein the plurality of driving lines on the sensor panel are simultaneously driven at the plurality of stimulation frequencies with a plurality of inherent distributions sequentially. The method, Storing the plurality of values after simultaneously applying the plurality of stimulation frequencies to the plurality of drive lines of the sensor panel with a plurality of inherent distributions How to include more. 8. The method of claim 7, further comprising calculating and storing drive line results for each drive line and each of the plurality of demodulation frequencies using the stored plurality of values for each of the plurality of sense lines. How to. 8. The method of claim 7, wherein the plurality of demodulation frequencies is a selected low noise frequency. 7. The method of claim 6, further comprising obtaining the plurality of values during a vertical blanking step of a liquid crystal display (LCD) adjacent the sensor panel. An apparatus for obtaining a plurality of values used to generate an image of a touch from a touch sensor panel, Includes a plurality of sensing channels, Each sensing channel is A charge amplifier configured to receive signals from different sense lines of the touch sensor panel, A multiplexer coupled to the output of the charge amplifier, A plurality of mixers connected to the output of the multiplexer, One frequency generator circuit coupled to each of the plurality of mixers and generating demodulation frequencies, and One accumulator connected to each of the plurality of mixers, the accumulator generating a value representing an accumulated mixer output. Including, Each frequency generator circuit in each sense channel generates a different demodulation frequency, the different demodulation frequencies corresponding to different stimulus frequencies applied simultaneously to the drive lines of the touch sensor panel, and the different stimuli Wherein the frequency includes both positive and negative phases of at least one of the stimulus frequencies. 12. The apparatus of claim 11, wherein at least one of the frequency generator circuits comprises a numerically controlled oscillator (NCO). 12. The apparatus of claim 11, further comprising a memory to store the plurality of values generated by each sense channel. 15. The apparatus of claim 13, further comprising a processor for each of the plurality of sense lines, using the stored plurality of values to calculate and store a drive line result for each drive line and each of the plurality of demodulation frequencies. . A computing system comprising the apparatus of claim 11. A mobile telephone comprising the computing system of claim 15. A digital audio player comprising the computing system of claim 15. A method of operating a touch screen having a touch sensor panel and a display device, Updating the display device during the active period of the display device, and Simultaneously applying a plurality of stimulation frequencies to the touch sensor panel to obtain an image of a touch from the touch sensor panel during a vertical blanking step of the display device, wherein the plurality of stimulation frequencies are plus and at least one of the stimulation frequencies; Include all negative phases- How to include. 19. The method of claim 18, wherein the display device is a liquid crystal display (LCD). A system for obtaining a plurality of values for generating an image of a touch from a touch sensor panel, A touch sensor panel having a plurality of drive lines and a plurality of sense lines, and An integrated circuit connected to the touch sensor panel Including, The integrated circuit, Driver logic configured to generate a plurality of stimulus signals in the plurality of drive lines, the driver logic including a charge pump configured to convert a low level supply voltage for the integrated circuit into a high level supply voltage, the driver logic also being in the high level Configured to convert the supply voltage into a stimulus signal of reduced amplitude; and A plurality of sense channels, each sense channel comprising a charge amplifier configured to receive sense signals from different sense lines of the touch sensor panel, the plurality of sense channels generating the plurality of values from the received sense signals. The plurality of values represent a plurality of accumulated mixer outputs. Including; Wherein each charge amplifier in each sense channel includes a reduced feedback capacitance, the physical size of which is reduced as a low amount of charge is injected into the sense line by the reduced amplitude stimulus signal. The method of claim 20, wherein each sensing channel is A multiplexer coupled to the output of the charge amplifier, A plurality of mixers connected to the output of the multiplexer, A frequency generator circuit coupled to each of the plurality of mixers and generating a demodulation frequency, and An accumulator coupled to each of the plurality of mixers, the accumulator generating a value representing the accumulated mixer output More, Each frequency generator circuit generates a different demodulation frequency, the different demodulation frequencies corresponding to different stimulation frequencies applied simultaneously to the drive lines of the touch sensor panel. 22. The system of claim 21, wherein at least one of the frequency generator circuits includes a numerically controlled oscillator (NCO). 22. The system of claim 21, further comprising a memory to store a plurality of values generated by each sense channel. 24. The method of claim 23, further comprising a processor for calculating and storing drive line results for each drive line and each of the plurality of demodulation frequencies using the stored plurality of values for each of the plurality of sense lines. system. A computing system comprising the system of claim 21. A mobile telephone comprising the computing system of claim 25. A digital audio player comprising the computing system of claim 25. A method of obtaining a plurality of values for generating an image of a touch from a touch sensor panel, Converting a low level supply voltage for the integrated circuit to a high level voltage using a charge pump in the integrated circuit, Generating a reduced amplitude stimulus signal in the integrated circuit using the high level voltage, wherein the reduced amplitude stimulus signal is for driving a plurality of drive lines in a touch sensor panel; Receiving a sense signal from each of the plurality of sense lines in the touch sensor panel with a charge amplifier in each of the plurality of sense channels in the integrated circuit, the plurality of sense channels generating the plurality of values from the received sense signals. Wherein the plurality of values represents a plurality of accumulated mixer outputs, and Using a reduced feedback capacitance in each charge amplifier, the physical size of the capacitance being reduced as a low amount of charge is injected into the sense line by the reduced amplitude stimulus signal. How to include. The method of claim 28, Demodulating the received sense signal in each sense channel using a plurality of different demodulation frequencies, wherein the different demodulation frequencies correspond to different stimulus frequencies applied simultaneously to the drive lines of the touch sensor panel; , And Accumulating the demodulated sense signals in each sense channel to produce the plurality of values. How to include more. 30. The method of claim 29, further comprising generating a demodulation frequency that demodulates the received sense signal using one or more numerically controlled oscillators (NCOs). 30. The method of claim 29, further comprising: storing the plurality of values generated by each sense channel, and for each of the plurality of sense lines, each drive line and the plurality of demodulations using the stored plurality of values. Calculating and storing drive line results for each frequency. A mobile telephone comprising an apparatus for obtaining a plurality of values used to generate an image of a touch from a touch sensor panel, The apparatus includes a plurality of sense channels. Each sensing channel is A charge amplifier configured to receive signals from different sense lines of the touch sensor panel, A multiplexer coupled to the output of the charge amplifier, A plurality of mixers connected to the output of the multiplexer, One frequency generator circuit coupled to each of the plurality of mixers and generating demodulation frequencies, and One accumulator connected to each of the plurality of mixers, the accumulator generating a value representing an accumulated mixer output. Including, Each frequency generator circuit in each sense channel generates a different demodulation frequency, the different demodulation frequencies corresponding to different stimulus frequencies applied simultaneously to the drive lines of the touch sensor panel, and the different stimuli Wherein the frequency comprises both positive and negative phases of at least one of the stimulus frequencies. A digital audio player comprising a device for obtaining a plurality of values used to generate an image of a touch from a touch sensor panel. And a plurality of sensing channels. Each sensing channel is A charge amplifier configured to receive signals from different sense lines of the touch sensor panel, A multiplexer coupled to the output of the charge amplifier, A plurality of mixers connected to the output of the multiplexer, One frequency generator circuit coupled to each of the plurality of mixers and generating demodulation frequencies, and One accumulator connected to each of the plurality of mixers, the accumulator generating a value representing an accumulated mixer output. Including, Each frequency generator circuit in each sense channel generates a different demodulation frequency, the different demodulation frequencies corresponding to different stimulus frequencies applied simultaneously to the drive lines of the touch sensor panel, and the different stimuli Wherein the frequency comprises both positive and negative phases of at least one of the stimulus frequencies.

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